Check for register clobbers when merging a vreg live range with a
reserved physreg in RegisterCoalescer.

Previously, we only checked for clobbers when merging into a READ of
the physreg, but not when merging from a WRITE to the physreg.

Differential Revision: https://reviews.llvm.org/D28527

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@291942 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed